Programmable number lock system

Programmable number lock system is a high security number lock system that can be used to lock electronic devices. The present system is very user friendly. This system is a combination of software and hardware at its best. We have used a 8051 microcontroller kit for interfacing our system.

In the present design we can activate or deactivate 9 devices. Each device is locked using a 4 digit code (password). The code can be set as per the user’s desire, hence the name ' PROGRAMMABLE '. For the device to be activated (unlocked), the user should enter the code that had been entered when the device was locked. In case the user enters the wrong code a silent alarm will be activated.

Introduction to Programmable number lock system:

The system has three units, namely:

( i ) Keyboard unit.

( ii ) Display unit.

( iii ) Control unit.

The keyboard unit consists of 9 number keys, 1 unlock key and 1 lock key. These are all push button switches. This unit is used to select the desired device and to enter the codes into the system. It is also used to request the system to lock/unlock the selected device.

The display section contains 5 seven segment display. This unit displays the device number and the code entered. This section is detachable. If detached it does not affect the working of the whole system. This unit also contains password reset button and an LED to indicate the error when the device is already locked and user wants to lock the device again. The error indicator also indicates an error when the system is already unlocked and the user tries to unlock the same.

The control unit is the heart of our system. It contains the necessary circuitry for the control of the device .This unit controls 9 devices, which is lock/unlock by selecting it using the keyboard and entering the password. If the code entered to unlock the device is wrong, then a silent alarm is triggered .The keyboard unit and the display unit are connected to this unit.

All these three units are merged together to form the whole system.

Block diagram of Programmable number lock system:

Working of the system:

When the system is initially installed the reset button is pressed. This key is present in the control unit. This unlocks all the devices. This is to avoid undesired functioning of the system.

To lock a particular device the device number is selected using the keyboard. Once the device is selected the user has to press the lock key present in the keyboard. Now the device waits for the user to enter the the code. The user can enter a 4 digit number using the keyboard as per his desire. Once all the 4 digits are entered the system electronically locks the selected device.

In the same manner to unlock a particular device, the device number is entered using the keyboard. Once the device number is selected the code for the selected device is entered. If the entered code matches the code that had been entered while that particular device was locked then the selected device will be activated (unlocked). If the codes do not match each other a silent alarm will be triggered (a LED placed in the control section. Shown in figure 3).An error indicator (placed in the display section) is provided if any user tries to lock a device which has already been locked or vice versa.

If the user is half way entering the code or has done an error while entering the code and wants to start over all again then a reset button is provided in the display section. By pressing this button the user can start from entering the device number and so on.

The number of devices which the system can control can be increased by addition of a few components in the control unit. More security can be achieved by increasing the number of digits in the code. This can be done by minor changes in the program. The system uses the internal RAM of the 8051 to store the code and hence puts a lower limit to the number of digits in the code and also the number of devices the system can control. Once the system is installed only the display unit and keyboard unit will be accessible to the user. Access to the control unit should be provided only to an official personal since it contains the system reset button.

System:

In this section we will be explaining the hardware design these units individually. Each unit description is accompanied by its circuit diagram.

KEYBOARD UNIT :

The keyboard used in this system is an encoder type. It uses IC 74147 priority encoder to convert the entered the digits to its corresponding binary codes. IC 74147 has a active low inputs as well as active low outputs (for more details please refer the corresponding data sheets). Each of the pins are activated using push to on switches. These switches ground the encoder inputs to activate that particular number giving the equivalent BCD code. This is then given as input to IC 7404 which is an inverter. To avoid loading of 7404 by the later stages transistor switches are provided to each of its outputs. The circuit diagram of the keyboard is as given in the next section.

The logic used here is shift and display i.e. when the next number is entered the previous number is shifted to the left by one unit and then the next number is displayed. To achieve this we have used IC 7496 which is a 5–bit shift register (for more details please refer the corresponding data sheets). The data lines from control section are given serially to the registers as shown in the circuit. The clock to these registers is given by the program every time a button on the keyboard is pressed. The shifting used here is parallel shifting. The outputs of the registers are given to CD4511 BCD to seven segment decoder. The seven segment display used are common cathode type since the output of the decoder is high when activated. This section consists of a reset switch which is used to reset the display.

Control Unit

APPLICATION:

The ‘Electronic device number lock’ system is a high security system.The main application kept in mind during the design of this system is to secure expensive electronic devices and machinery. The access to such devices can be restricted to particular users only. The system is highly secured since the code can be changed every time the user locks it. This can also be used an physical lock by using solenoid and thus can be used to lock safes in banks or other institutions. Regular electronic number lock available in the market can lock/unlock just one device, but this design can lock/unlock up to nine devices.